It has become common practice to provide remote message or call boxes which are connected by radio transmitters with a central receiver that directs incoming messages from the various boxes to a base station. The receiver may be adjacent the base station or spaced therefrom in accordance with standard design considerations. Also, the call boxes or message boxes could be coupled with the receiver by telephone wires or microwave transmission channels in accordance with well known practices. Irrespective of the system structure, the various remote call boxes or message boxes transmit messages to the base station in accordance with conditions at the various call boxes. These call boxes can be street boxes of the type used in fire alarm systems or master boxes of the type used in monitoring certain specific areas of an industrial facility. One of the most widely observed examples of a call box is the motorist air call box located along highways. These boxes can be actuated to indicate a need for police, ambulance, a tow truck or other motorist assistance items. In all instances, the remote call boxes create a message which is indicative of a condition or a change in condition at the call box. For instance, if a fire alarm is manually or automatically activated, a street box will create a message that is transmitted to a base station to identify the box and the type of signal or change of condition being reported. In many systems, the base station monitors street boxes, master control boxes and motorist aid boxes all from a single console. The messages are contained on a series of AM tones which are transmitted in serial fashion to the base station from the remote call boxes. In the past, three to five tones have been employed to provide the address of the particular call box. One or two tones in the message being transmitted are used to indicate the particular function which is being reported by the transmitted message. Consequently, the tone coded message transmitted by the activated call box included tone signals indicative of the box number together with tones indicative of the type of function being reported. Sine there are certain standard functions which are incorporated in all call boxes, such as fire, test and tamper, and some functions normally committed, such as police and ambulance, there was heretofore very little available space on the message to report other functions. Thus, the intelligence transmitted from the call box was somewhat limited. The messages of the prior systems employed digits to identify and locate the box and digits for functions.